This invention relates to a redundant wiring apparatus and a method of making the same. The invention also relates to a redundant wiring apparatus and a method of making a redundant wiring apparatus used for a thin film transistor array substrate of a flat panel display device, e.g., a liquid crystal display device.
Recent development of such a liquid crystal display device has focused on the features of small size, light weight and low power consumption. The liquid crystal display device includes a thin film transistor array substrate, a counter substrate and a liquid crystal layer held between the array and counter substrates. The array substrate is provided with an insulation substrate on which a plurality of signal lines and scanning lines are formed in matrix. Pixel electrodes are disposed in the region defined by the signal and scanning lines. The thin film transistors are formed as switching elements in the vicinities of the crossing points of the signal and scanning lines, respectively, and are connected with them through the pixel electrodes. The counter substrate, on the other hand, includes an insulation substrate to which counter electrodes made of transparent conductive films are attached.
The signal and scanning lines are extended out of a display region and are connected with electric power supplying electrodes formed at the surrounding edges of the array substrate. The electric power supplying electrodes are further connected to driver circuits provided outside the array substrate.
In the liquid crystal display device of this sort, it has been recently required that a peripheral frame portion of the display region is made as narrow as possible (the "narrow frame") to ensure the wide display region. Further, it is necessary to reduce the manufacturing cost and also to improve the production yield.
Where the liquid crystal display device, however, includes the narrow frame, spaces allocated to wires drawn from the display region are so limited that the wiring width and gap become narrow. As a result, open- and/or short-circuited wiring troubles are apt to easily take place in manufacturing.
To improve the reliability by preventing from such open-circuited wiring, a liquid crystal display device which has been available in the market includes signal lines drawn from the display region provided with a redundant, two-layer (parallel) wiring structure. The signal line consists of first and second laminated wires between which an insulation layer is held. Connectors passing through perforations in the isolation layer are provided to connect the first and second wires at both ends located in the display and near the connecting pads, respectively. Thus, with the structure, the signal lines are kept conductive even in the event that either one of the first and second wires is open-circuited. It improves the reliability on the signal lines.
Although the structure prevents the wires from being open-circuited, the short-circuited wiring trouble occur twice as many as that with single wire structure due to redundant wires. In the case of a liquid crystal display device with the narrow frame, the spaces allocated to the lead wires drawn from the display region are so narrow that short-circuited wiring troubles take place more readily.
It is quite difficult not only to detect apoint where such a short-circuited wiring trouble takes place but also to cut it. It is one of the critical factors to automate manufacturing processes of a liquid crystal display device.